The invention relates to a machine for printing or otherwise decorating hollow bodies such as sleeves, collapsible tubes, cans or the like comprising
a rotationally driven decoration application drum, which is peripherally provided with one or more decoration applying faces, which on rotation of the decoration application drum proceed along a first circular orbit,
a rotationally driven capstan plate whose axis of rotation is arranged athwart that of the decoration application drum, said capstan plate bearing capstan units arranged in sequence at a distance apart in its direction of rotation, said units being respectively provided with a receiving capstan, onto which capstan a hollow body to be decorated may be respectively slipped, the radially outwardly directed sections of the slipped on hollow body proceeding along a second orbit on rotation of the capstan plate,
and orbit correction means, which ensure that during a passage, occurring with a simultaneous decoration operation, of a decoration zone associated with the peripheral region of the decoration application drum, the capstan units are so shifted by performing a follow-up movement directed athwart the axis of rotation of the capstan plate that the second orbit coincides with the first orbit, the capstan units being moved respectively on guide means provided on the capstan plate in the direction of the follow-up movement and being connected with cam following means which on rotation of the capstan plate run along a cam responsible for the follow-up movement.
Machines of this type, as for instance disclosed in the patent publication WO 97/07979, serve for printing or otherwise decorating hollow bodies having a round shape such as sleeves collapsible tubes, cans or the like. The term xe2x80x9cdecorationxe2x80x9d is in the present context to mean for instance measures for lacquering, labeling, foil embossing or screen printing as well. The respective machines possess a capstan plate driven for rotation, which is provided with capstan units arranged in sequence in the direction of rotation and which possess receiving capstans, on which the hollow bodies are held. Adjacent to the capstan plate there is also a rotationally driven decoration application drum, also driven to rotate, which is provided peripherally with one or more normally segmented decoration facesxe2x80x94in the case of printing machines it will be a question of printing facesxe2x80x94which on the rotation of the decoration application drum are moved along a first circular orbit, which extends between the decoration application drum and the capstan plate.
The hollow bodies held on the receiving capstans are also moved through the decoration zone on rotation of the capstan plate. Then the radially outwardly facing sections of the so mounted hollow bodies proceed along a second orbit and in the decoration zone are brought into contact with the decoration face there at the same time. It is in this manner that it is possible for example for colored ink to be applied to the hollow bodies.
Since the two above mentioned orbits are oppositely curved, in continuous decoration methods, which are more particularly employed at high rates of production, correction of the second orbit is required in order to match its form, on its rapid passage through the decoration application zone, to the first orbit there of the first orbit. For this purpose the system of the said patent publication WO 97/07979 causes the capstan units to be guided by several guide rails so that they are able to be radially moved on the capstan plate. Simultaneously roller-like cam following means, which are pivotally mounted on a capstan support of the capstan units, engage a cam of such a shape that the capstan units perform a follow-up movement, which is athwart the axis of rotation of the spindle plate, on passage through the decoration zone, such movement matching the shape of the second orbit to that of the first orbit.
One problem occurring with the known machines of the type initially mentioned resides in the relatively high wear rate of the means provided for orbit correction of the capstan units. The forces coming into play during a decoration operation and acting on the receiving capstan give rise to a tilting moment which thrusts the cam follower rollers, arranged directly on the capstan supports, more strongly against the cam. Furthermore, heavy bending moments act on the guide rails of the capstan support. All in all this means that the accuracy of mechanical control and guidance is reduced with time and accordingly the quality of the decoration operation suffers therewith.
One object of the invention is to create a machine of the type initially mentioned in the case of which the components partaking in orbit correction are less prone to wear.
In order to achieve these and/or other objects appearing from the present specification, claims and drawings, in the present invention its inner side facing the axis of rotation of the capstan plate, of each capstan unit at a distance from the same a pivot shaft is provided which is parallel to the associated receiving capstan and is mounted for rotation as regards its longitudinal axis, said pivot shaft bearing the cam follower means at a radial distance from its longitudinal axis and on which, also at a radial distance from its longitudinal axis, has a pitman means pivoted on it, said pitman means at its other end engaging the capstan unit, so that a rotary movement caused by the cam follower means of the pivot shaft is responsible for the follow-up motion of the respective capstan unit with the aid of the pitman means.
The correction of the second orbit on motion through the decoration zone is now caused because the pivot shaft is turned through a certain angle, the torque or moment exerted being dependent on the distance between the longitudinal axis of the pivot shaft and the cam following means engaging same. The rotary movement of the pivot shaft leads to a pivotal movement of the pivot point of the pitman means so that the latter, dependent on the direction of rotation, is drawn inward or thrust outward in order to shift the associated capstan unit and to maintain the follow-up movement. In addition to the high precision thus achieved of the orbit correction there is simultaneously an effect such that the forces applied during the decoration operation do not act directly on the cam following means and the cam associated with same, but at least for a major extent are taken up by the pivot shaft and its bearing means. To the extent that a moment is exerted by the decoration forces by way of the pitman means on the pivot shaft, it is possible, by suitable matching of the working lever arms, to ensure that the resulting forces, thrusting the cam following means against the cam, are at a low level. All in all it is accordingly possible for the wear occurring on moving parts to be substantially reduced, something rendering possible high quality performance decoration even after a long working life.
Further advantageous developments of the invention are defined in the claims.
It is convenient for each capstan unit to possess an associated capstan plate bearing the associated receiving capstan by way of which the unit is rotatably supported on the capstan plate. In this case the receiving capstans may be mounted for rotation on the associated capstan plate, something which during the application of decoration allows rotation about the respective axis and accordingly free rotary movement of the hollow bodies on the capstan even if there is substantial friction between such bodies and the receiving capstans. Preferably, in this case each receiving capstan is provided with rotary drive means, with which during the decoration operation enables rotary movement to be caused, something which for example renders possible an extremely accurate development of the printed image during a printing operation.
The pitman means cooperating in the production of the follow-up movement best comprises at least two, and more particularly just two, pitman arms extending between the capstan unit and the pivot shaft, which are spaced apart in the axial direction of the pivot shaft and more especially engage the front and rear terminal parts of any capstan support present. Having such a parallel arrangement of the two pitman arms leads to a support means which is extremely dimensionally stable and capable for ensuring an accurate guiding action. The pitman arms may be respectively a component of a independent pitman unit.
In accordance with a preferred development of the invention the pitman means articulate, or have a pivotal connection, with the respectively associated capstan unit, the pivot axis extending in parallelism to the longitudinal axis of the capstan unit or coinciding with it. In the latter case it is more particularly possible to arrange for the pitman means to pivotally surround the associated capstan unit, this leading to a particularly compact overall size.
An other preferred feature of the invention is such that the bearing and guiding measures provided for rendering possible the follow-up movement of the capstan units are provided generally at the same level as the longitudinal axis of the respective receiving capstan, it being possible for each capstan unit to be secured in the direction of rotation of the capstan plate by means of support means secured to the capstan plate. Since in this case the guidance means are practically at the same level as the point of application of the decorating forces, an extremely accurate guidance is possible while substantially eliminating tilting forces. Furthermore, such measures effectively suppress vibrations.
In the case of a design whose performance quality is even further improved it is possible for the machine to be additionally provided with temporary offsetting means, by which the receiving capstans may be temporarily shifted out of their normally assumed home position in a radially inward direction into offset position so that the second orbit is spaced from the first orbit on moving through the decoration zone. This renders possible an individual offsetting or temporary shifting of the receiving capstans from the decoration application drum, if owing to some trouble condition or another cause the respective receiving capstan does not bear a correctly mounted hollow body or any body at all. Without offsetting there would be a danger of the decoration operation being performed on a naked receiving capstan. Owing to such temporary offsetting it is possible for a sufficiently large distance to be ensured in order to prevent contact between the decoration application drum and a receiving capstan.
It is convenient for the offsetting movement produced by the offsetting means to be performed by the capstan units bodily. Whereas in the case of the said patent publication WO 97/07979 a brief rotary movement of the eccentrically mounted receiving capstans meant that only such receiving capstans alone were offset, something which necessitated a separate offsetting drive, in the present invention components of the orbit correction means may also be utilized for offsetting of the receiving capstans.
In the present case the offsetting movement of the receiving capstans is preferably caused by a radial displacement of the pivot shaft. The offsetting means may, for each capstan unit, comprise an offsetting part mounted on the capstan plate for rotation about an axis parallel to the longitudinal axis of the associated receiving capstan, on which offsetting part the associated pivot shaft is eccentrically mounted for rotation with a parallel axis of rotation. Additionally provided actuating means may here cause a turning of the offsetting part in relation to the capstan plate and to the associated pivot shaft in order to position the offsetting part in two different -angular positions, in which the pivot shaft is at different distances from the axis of rotation of the capstan plate.
A particularly compact design and with a small mass to be moved is produced if the offsetting part is in each case in the form of a hollow shaft which at least partially surrounds the pivot shaft.
The angular settings of the offsetting part may be set by spring means, it being possible to employ a snap-action mechanism which ensures that one and the same spring means may set both angular positions.
In order to move the offsetting part into an angular position producing the offset position of the associated receiving capstan, an actuator may be present, which is activated by a sensor means, which is responsive to the state of the receiving capstans prior to reaching the decoration zone.